High resolution mega-pixel cameras use a focusing function to take high quality pictures. Most Auto-focusing methods involve mechanical moving parts such as step motors which add complexity in hardware and software design. Electro-wetting liquid lenses and liquid crystal lenses belong to the category of adaptive optics, where the optical wave front is adjusted without the aid of mechanical movement. In the case of the liquid crystal lens, the optical wave-front change is achieved through a gradient change of a refractive index which is electrically tuned by an external voltage. Even though adaptive optics might avoid the use of mechanical moving parts, existing camera arrangements and imagers using adaptive optics have issues and challenges for implementation in an auto-focus type camera.
As noted above, mechanical parts are generally used with cameras having auto-focus features. Several U.S. patents discuss the use of adaptive optics using liquid crystal lenses, but fail to address issues with polarization and birefringence that result from using liquid crystal lenses. Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on the polarization of the light. Polarization is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. More generally, the polarization of a transverse wave describes the direction of oscillation in the plane perpendicular to the direction of travel.
For example, U.S. Pat. No. 5,359,444 discusses a conceptual liquid crystal lens based eyeglass with auto-focus that failed to address polarization and birefringence issues from the liquid crystal material. Likewise, U.S. patent application 2006/0164732 A1 proposed a liquid crystal lens for optical zooming and U.S. Pat. No. 5,815,233 proposed a system level of liquid crystal lens for optical information processing for coherent light application. Each failed to appropriately address polarization and birefringence. A publication sponsored by the National Academy of Sciences (0600850103), published on Apr. 18, 2006 discusses the use of a diffractive liquid crystal lens to implement eyeglass auto-focus.